Handle source changes

index.js

@@ -14,12 +14,14 @@ const wrapValueAsOption = require("@validatem/wrap-value-as-option");
 
 // FIXME: Update other stream implementations to new API
 module.exports = function simpleSinkStream(_options) {
-	let { onResult, onEnd, onAbort } = validateOptions(arguments, [
+	let { onResult, onEnd, onAbort, onSourceChanged } = validateOptions(arguments, [
 		required,
 		wrapValueAsOption("onResult"), {
 			onResult: [ required, isFunction ],
 			onAbort: [ isFunction ],
+			onSourceChanged: [ isFunction ],
 			onEnd: [ isFunction, defaultTo.literal(function defaultOnEnd() {
+				// FIXME: Deprecate this, it does not work as-expected when the onResult callback never gets called (eg. due to a stream immediately terminating), as the onResult callback will then never get a chance to set the lastResult, not even to an initializer value (eg. an empty array for `collect`)
 				// We return whatever value we got last from the specified onResult callback.
 				return lastResult;
 			})]
@@ -30,8 +32,10 @@ module.exports = function simpleSinkStream(_options) {
 	let onEndCalled = false;
 	let onEndResult;
 	let abortHandled = false;
+	let lastKnownSource;
 
 	return {
+		_promistreamVersion: 0,
 		description: `simple sink stream`,
 		abort: propagateAbort,
 		peek: propagatePeek,
@@ -50,9 +54,15 @@ module.exports = function simpleSinkStream(_options) {
 			}
 
 			return Promise.try(() => {
+				if (source !== lastKnownSource && onSourceChanged != null) {
+					lastKnownSource = source;
+					return onSourceChanged(source);
+				}
+			}).then(() => {
 				return attemptRead();
 			}).catch(isEndOfStream, () => {
 				/* Don't attempt to do another read, we're done.  */
+				// FIXME: Is it actually correct to keep returning the same thing?
 				if (onEndCalled) {
 					return onEndResult;
 				} else {